[Diagnosis of maternofetal infections].

Prevention is an essential aspect of management of infections that can be transmitted from mother to fetus during pregnancy: The prescription and interpretation of serologic markers differ according to clinical context: screening, counts, clinical signs, or ultrasound signs. Testing for rubella IgG antibodies is recommended at the beginning of pregnancy, in the absence of written results proving either immunity or previous vaccination with two doses. Monthly serologic monitoring (IgG and IgM) is recommended for woman lacking immunity to toxoplasmosis. Diagnosis of a primary infection requires the concomitant detection of IgG and IgM. Nonetheless, the presence of specific IgM is not necessarily a marker of recent infection. IgG avidity must be measured to confirm or rule out a recent primary infection when IgM is positive. The observation of stable antibody titers is often inaccurately considered to be reassuring. In fact, depending on the individuals tested and especially the technique used, antibodies may reach a plateau several days or several weeks after the onset of the infection. Clinical diagnosis of rubella is not reliable, and its rarity today means that physicians are unlikely to recognize it or consider it as a possible differential diagnosis. Nonetheless, residual circulation of the rubella virus continues in France. A chickenpox rash is diagnosed clinically. For atypical eruptions, the virus can be sought directly in the vesicular fluid. Serology is not helpful in this case.